I'm pretty new to the art of photography so I hope you can help me. I am trying to take a photo where the flash falls off completely leaving the subject in the foreground and the background completely black. I am currently using a Fuji S6500fd, what conditions would I need to get this to work properly and how would I set up my camera to do this? Although I obviously don't have all the features and modes of big people's cameras.
Thanks
The power of the flash falls off according to the "inverse square law". That means that each time you double the distance to your subject the light becomes only 1/4 the strength at the closer distance. 1/4 is 2 stops.
So, let's say the distance to your subject is 4' and the background is 8' away. The background will be 2 stops darker than your subject. If you can double the distance to the background again, to 16', it will become 4 stops darker than your subject. If your background is no brighter than middle grey it will look pretty dark at that point.
Your simple choices are either to use a dark backdrop in the first place, and/or place the background as distant as you can from the light source, compared to your subject.
As has previously been stated, if you use the fastest shutter speed possible, for your flash, you will minimise the impact of ambient lighting falling on the background (and the subject). If you close the aperture down and pick a low ISO you will make the flash work harder (this is where the guide number is important), but so long as it is powerful enough your subject will be lit correctly and the background should disappear to blackness.
EDIT : I was trying to locate a good reference example, which I've seen before, but yesterday the critical example image was not loading for me. Anyway, the picture that goes with item #3 here -
http://photography-on-the.net/forum/showthread.php?t=171657 seems to demonstrate the fall off well. There may be some other useful stuff there as well.